Ripe pear fruit did not freeze while still on tree at 18F

[T.G.G. Moogly]

It went down to 18 degrees F last night. We've had half a dozen nights where the temps dropped into the mid twenties and more where it hit freezing. Also have had a ton of frost nights.

So I noticed a ripe pear, Kiefer, still on the tree that I had overlooked. Has a small wormy spot but because it is such a large fruit there's plenty to eat. I noticed it and picked it this morning when the temperature was 21F. I brought it in and set it on the counter expecting to find mush by afternoon. But it is perfect, not frozen!

I googled some questions and it says that pears resist freezing depending on the variety and the degree of ripeness. This baby is definitely fully ripe, large and must be the proper variety that it could hang on the tree about all winter, or at least to 18F. I think that's incredible.

My dad's orchard had an apple variety that we just called Winter Apple. You could pick these things thru the winter as they didn't fall from the tree like all the others. So there must be some kind of natural antifreeze in some ripe fruits. Cool.

 

[bilby]

It went down to 18 degrees F last night. We've had half a dozen nights where the temps dropped into the mid twenties and more where it hit freezing. Also have had a ton of frost nights.

So I noticed a ripe pear, Kiefer, still on the tree that I had overlooked. Has a small wormy spot but because it is such a large fruit there's plenty to eat. I noticed it and picked it this morning when the temperature was 21F. I brought it in and set it on the counter expecting to find mush by afternoon. But it is perfect, not frozen!

I googled some questions and it says that pears resist freezing depending on the variety and the degree of ripeness. This baby is definitely fully ripe, large and must be the proper variety that it could hang on the tree about all winter, or at least to 18F. I think that's incredible.

My dad's orchard had an apple variety that we just called Winter Apple. You could pick these things thru the winter as they didn't fall from the tree like all the others. So there must be some kind of natural antifreeze in some ripe fruits. Cool.

It's called 'sugar'.

Sucrose is quite an effective antifreeze.

 

[steve_bank]

So, you are eating a natural antifreeze? Will eating the pears keep you from freezing?

 

[lpetrich]

We're warm-blooded, and that means that our body temperature cannot safely go much more than its normal value, 37 C (98.6 F). These sources define hypothermia as a body temperature below 35 C (95 F) -- not much lower.

• Hypothermia - Symptoms and causes - Mayo Clinic
• Hypothermia: Signs, Symptoms, Causes, and Treatment - the same threshold.
• Hypothermia|Winter Weather

Cold-blooded species can be active in temperatures below freezing by making antifreeze proteins.

 

[bleubird]

I think ripe fruit has some alcohol,also. That help drop the freezing temp.

 

[T.G.G. Moogly]

Thanks for all the replies! One possibility I considered is that because this tree is growing near a road that the microclimate around it kept it from freezing, that the pavement absorbed heat and protected it from freezing. I still have not ruled that out but it doesn't seem like that was the reason. I had water bottles in the trunk of my car and they were frozen solid that morning right beside the tree.

One thing is certain, every googled answer has been wrong on the subject.

 

[steve_bank]

If you want to pursue it there are small low mass temperature sensors you can insert into the fruit. RTD sensors are cheap and you only have to measure resistance with a meter.

Is a tree trunk warmer than air temp? You could measure the temp around the tree.

 

[T.G.G. Moogly]

I wrap the fig trees every year and keep a sensor inside one tree that I can read from my phone. It registered 22.1F that night, which was inside the insulating cover and getting a bit of ground warmth. But I like the idea of a sensor that is inserted in the fruit.

And I ate the pear today after it sat in the fridge for five days. It was delicious, the wormy spot was mostly cosmetic. It was not as sweet as I thought it would be even though it was definitely fully ripe. I suppose it is the variety.

I remember watching a show about life in the Antarctic under the ice. Certain fish have evolved a mechanism whereby water crystals are surrounded by something that keeps the rest of the fish from freezing. It could very well be that something in the fruit does the same thing, preventing water from crystallizing. It actually seems that must be the case. It's weird though. If I put fruit or fruit juice in the freezer it freezes solid. It's a good mystery.